The invention relates to a device for adjusting light intensity provided by a lamp to a fiberoptic light transmission system. Particularly, the invention relates to a dimmer controllably intercepting a beam of light to regulate light flux impinging on the entrance of a fiberoptic conductor. More particular, the invention relates to a three dimensional dimmer controllably adjusting light which is transmitted through it to a fiberoptic conductor from a light source used for illuminating a bodily cavity during an endoscopic surgical operation.
Fiberoptic systems used in endoscopic surgery for illuminating an interior of a cavity have become practically indispensable in various surgical procedures. One of the primary reasons for such widespread use of a fiberoptic system is its flexibility allowing a surgeon to illuminate and, thus, to observe inside regions of the bodily cavity that are not easily accessible. Typically, a fiberoptic conductor includes a multiplicity of light conducting fibers, e.g. glass fibers, in the form of a bundle or strand, and extends between an entrance plane and an exit plane which is placed near the site that is to be illuminated.
Fiberoptic systems typically utilize a high intensity lamp as a light source in endoscopic procedures. Too high or too low an intensity of light can detrimentally affect the vision of a surgeon or imaging device. As a consequence, control of the luminous intensity at the exit plane of a fiber conductor has gained a particular significance in the endoscopic surgical procedures. Particularly, the ability to adjust intensity of the light without its distortion becomes critically important.
Numerous attempts have been made to vary the luminous intensity or light-flux from the lamp""s output. Typically, these attempts have involved changing the feeding current or voltage or phase of the light source. This control, however, is typically accompanied with changes in the color temperature of the light source and, thus, the color of the illuminated object. The latter is particularly disadvantageous if the image is to be photographed or transmitted or recorded by video techniques, as well as making tissue color determination essential in disease diagnosis, difficult or impossible.
To solve the color change problem, attempts have been redirected to influence illumination of a cavity by introducing a mechanical dimming device or dimmer which is arranged in the optical path between a light source and the entrance plane of a fiberoptic conductor. Utilization of mechanical control devices basically obviates the necessity for interference with the power supply of the light source and eliminates the color temperature change of the emitted light.
Typically, a dimmer is a two-dimensional disk-shaped element which is controllably displaceable along the optical path to alter the light flux impinging upon the entrance plane of a fiber conductor. Displacement, which can be rotational and/or linear, leads to dimming the intensity of light provided to an optical fiber conductor by covering at least a portion of its entrance plane.
The conventional dimmer assembly suffers, however, from the problem that the control of the incident luminous flux causes a change in the course of passage of illuminating light entering the fiber conductor. This, in turn, leads to considerable variation in the light-distribution characteristics of illuminating light emanating from the conductor.
Still another problem characteristic of the conventional mechanical dimmer is that it may be impossible to avoid a change of the course of passage of illuminating light caused by a change in the luminous flux of light which enters a fiberoptic conductor. Therefore, when the luminous flux of illuminating light changes to a considerable extent upon entering a fiber conductor, a distinct change occurs in the light distribution and spectral characteristics of light at its exit plane.
Several attempts have been made to overcome these problems. Typically, a circular disk is placed perpendicular to the light axis and between a lamp and a fiber conductor. The disk may be perforated and have different arrangements of perforations designed to gradually block the light upon the disk""s displacement. Basically, this type of the mechanical dimmer is directed at a change in the aperture and has been favorably accepted in the endoscopic medical field.
U.S. Pat. No. 5,006,965 to Jones discloses a disk including an outer peripheral imperforate band and an inner perforate band which is provided with differently sized and variably spaced apart slots. The disk further has a part of its active length open so as when this open portion is in the path of the light beam, 100% of the latter is transmitted to an optical conductor. It is clear that the outer beam stops 50% of the beam, whereas the slots of the inner beam control the rest of the beam.
One of the problems this structure may pose is that a small amount of movement of the disk between its fully open and partly closed regions causes an abrupt and large change of the quantity of illuminating light. This is largely due to the fact that typically the disc may be quite large in proportion to the optical beam diameter.
Another problem associated with many types of planar circular dimmers including the one described above is that using such a disk may cause the outer edges of an output circle of the optical fiber to become smeared and later become dark, a phenomenon known as xe2x80x9cringingxe2x80x9d.
Still another problem of such structure is that a distribution of the output light is not monotonically variable throughout a substantial range of light-to-dark. Dimming the light incident on a fiberoptic light guide aperture requires that on the average all rays from all acceptance angles must be dimmed the same amount, as well described by Walter P. Siegmund (Walter P. Seigmund, Handbook of Optics (1978)). There are many ways to get a single perfect distribution of the output rays, however this xe2x80x9cperfectxe2x80x9d distribution is not monotonically variable negatively affecting illumination of a bodily cavity during an endoscopic surgical operation.
U.S. Pat. No. 4,233,650 to Hagner discloses a dimmer comprised of three diaphragms controllably displaceable with respect to one another to asymmetrically and unilaterally reduce the cross section of an entrance plane of a fiber conductor.
One of the obvious problems of this structure may be that a part of the entrance plane is always dimmed because the light beam is invariably blocked by inwardly extending vanes. In practical terms, however, a situation when a surgeon needs unhindered illumination of a cavity is quite frequent. Another problem associated with this structure is that a control mechanism regulating displacement of the three rings may be complicated. Still another problem is that the ringing phenomenon still may not be fully eradicated.
Many attempts have been made to use conventional optical diaphragms, such as an iris diaphragm. A problem common to many of these diaphragms is that they typically change the average entrance angle of the light into a fiberoptic conductor and the exit angle at its exit plane.
Referring to FIGS. 1a-1e, the results of various dimming schemes known in the prior art are shown. FIG. 1a shows the unblocked normal profile of a source of light.
FIG. 1b shows a diaphragm 12 crossing the center of the entrance plane of a fiberoptic conductor. It is clear that the light intensity is reduced all over a surgical area, and, particularly, a central region is totally dark
FIG. 1c illustrates a segment of the entrance plane being blocked. This structure imposes an upper limit on the light transmission, defined by the blocked sector.
Referring to FIG. 1c, disadvantages of an iris diaphragm mentioned above become clearer. Particularly, a beam width is reduced, thereby darkening peripheral regions of an illuminated surgical area while its central region may be disproportionately illuminated.
Finally, FIG. 1d illustrates a screen occluding part of an optical beam so as the central region of a surgical area is sharply illuminated by contrast with a darkened outer ring.
What is desired, therefore, is a dimmer that produces an output beam having substantially uniform intensity without a disproportionately illuminated center and/or dark peripheral regions. A dimmer having a substantial dynamic range of adjustment of light throughput, thereby eliminating a ringing phenomenon is also desirable. Further, a dimmer providing a constant light entry without reducing the maximum light flux emitted by the light source is also desirable, as is a three dimensional dimmer that produces monotonic dimming of a fiberoptic conductor.
With a dimmer in accordance with the invention, gradual adjustment of light throughput of a fiberoptic conductor can be dynamically performed by occluding fractions of an optic beam from a light source without developing a ringing phenomenon.
This is achieved with a dimming assembly in accordance with the invention by using a three-dimensional light-transmissivity shaper (also referred to as a dimmer) positioned along an optical path of light beam and projected in into a two-dimensional entrance plane of the fiberoptic conductor. To provide gradual adjustment of light throughput of the fiberoptic conductor, a dimmer has a compound geometrical shape symmetrical with respect to a plane of symmetry of the dimmer, which extends perpendicular to its axis of rotation. The rotation axis extends in the same plane as an optical axis of the light beam but perpendicular thereto.
In accordance with a cardinal concept of the invention, the dimmer is a solid body having an aspheric shape meaning xe2x80x9cshape with hornsxe2x80x9d or a wedge shape, if viewed along an optical axis, which is perpendicular to an axis of rotation of the body. The solid body is also mirror symmetrical about a plane of symmetry perpendicular to the axis of rotation and has substantially a semi-circular shape going from convex to concave, if viewed along the axis of rotation. Thus, the body may have an unlimited number of successive wedge-shaped axial planes terminating in the plane of symmetry. Therefore, each of the radial planes has a point spaced equidistantly from opposite axial ends, if viewed along the axis of rotation, and lying in the plane of symmetry.
Thus, the solid body continuously intercepts the beam of light and is shaped so that as it rotates each subsequent segment of the light beam is either greater or lesser than a previous segment, thereby achieving monotonically variable distribution throughout the greatest possible range of light-to-dark. This is achieved by a succession of axial planes each having a respective pair of opposite flanks outwardly diverging from the plane of symmetry and followed by another succession of axial planes, each having opposite flanks inwardly converging toward the plane of symmetry. Thus, an angle formed between the opposite flanks of each subsequent axial plane gradually increases, and then, upon reaching a 180 angle, gradually decreases along a cam surface of the dimmer. For the exception of one axial plane, each plane, thus, has either a nadir or an apex depending on whether the flanks diverge or converge with respect to the plane of symmetry.
The lesser angular distance between subsequent nadirs and apexes along the plane of symmetry the smoother an arc described by the plane of symmetry is, thereby gradually approaching Bezier transition between nadirs and apexes. As a consequence, the greater a number of subsequent radial planes is the more monotonic the distribution of light output is.
In accordance with a narrow aspect of the invention, the dimmer has a plurality of individual vanes. Each of the vanes has an outer side including a pair of flanks either converging toward the plane of symmetry or diverging therefrom to form a succession of apexes and nadirs.
Each embodiment, thus, has formations defining a configuration of a light transmission region depending upon an angular position of the rotation axis.
Thus, as the dimmer rotates, a path of light is intercepted by a series of smoothly shaped solid body or angularly spaced apart vanes defining a series of dimmed regions of an entrance plane of a fiberoptic conductor and producing substantially monotonic distribution of light output.
According to another feature of the invention, the dimming assembly may be provided with a device providing controllable rotation of a shaft and having a memory storing a variety of parameters which corresponds to positions of the axis of rotation wherein selective areas to be examined are best illuminated. If a surgeon decides that a surgical area has been best illuminated with one of the previously used segments or vanes, she can automatically rotate the dimmer until this desirable radial plane intercepts a light beam.
It is therefore an object of the invention to provide an endoscopic device including a dimming assembly which has minimal variations in light-distribution and spectral characteristics in response to changes of the luminous flux of illuminating light which enters a fiberoptic conductor.
Yet another object of the invention is to provide a rotatable dimming assembly having a solid cam body with a succession of adjacent segments which extend in a plane spaced radially asymmetrically from a rotation axis to controllably block the luminous flux of illuminating light without producing a ringing phenomenon.
Yet another object of the invention is to provide an endoscopic device with a dimming assembly having an array of differently shaped vanes which rotate about an axis extending transversely to an optical beam to controllably block the luminous flux of illuminating light without producing a ringing phenomenon.
It is still another object of the invention to provide an endoscopic device with a dimming assembly having a large dynamic range of adjustment of an output beam of light exiting a fiberoptic conductor.
A further object of the invention is to provide an endoscopic device with a mechanical dimming assembly that has a simple, reliable mechanism, which practically needs no maintenance.